The present invention concerns a device, that uses ions or neutrally charged gas to provide a thrust force or stream of matter. In particular, invention concerns a device that ejects matter with a jet form for use as an industrial plasma spray, industrial material processing, waste treatment, welding or cutting materials, or for plasma vapor deposition. The invention also concerns a device that can provide a propulsive thrust force for spacecraft propulsion, particularly an ion jet thruster, which uses an inertial electrostatic confinement design having a discharge plasma for generating ions that provide thrust when accelerated and expelled from the device in the plasma jet.
There is a well known need for an intense source of hot ionized or neutrally charged gas in a variety of industrial applications, such as plasma sprays for cleaning or etching surfaces and as plasma sources for sputtering or vapor deposition. Such a source could also be valuable for a range of applications that require an intense heat source, such as waste treatment or materials cutting and welding.
In another application, designers of spacecraft, particularly commercial satellites such as those used for telecommunications, are especially concerned with the cost per unit of "commercial payload" that is provided by their design. Giving the limited capacity of expendable rockets and the "space shuttle", severe size and mass limitations are placed upon the spacecraft design. Accordingly, the "commercial payload" for a communication satellite, such as one that would be launched into geostationary orbit to provide voice, data and television services, would include equipment, such as antennas, transponders, signal processing and switching equipment, which directly provide the communications service. In order to maximize the profitability of a given spacecraft design, the "commercial payload" must be maximized in order to provide the largest amount of revenue-producing capability. Because the remainder of the satellite concerns "overhead" structures and equipment such as the spacecraft body, solar cells, power system, thermal control systems and orbit steering thrust systems, the goal of maximizing the income-producing payload requires that the overhead payload must be decreased. Of course, the trade-off between "commercial payload" and "overhead payload" is affected by the need for efficiency and long life in connection with the overhead services provided on board.
The orbit steering thrust system for a spacecraft is important because it may be utilized for at least two purposes. One purpose is the maintenance of the spacecraft in geostationary or low/medium altitude Earth orbit or interplanetary flight paths. The thrusters impart a change of momentum which changes the velocity vector at a pre-determined point or segment of the trajectory.
The other purpose of thrusters is the function of actuators of a system for the maintenance of the spacecraft attitude or orientation. In the vacuum of space reaction forces are achieved by momentum changes. The rocket or jet method is well understood in the field. A further application for the propulsion system is the injection of the spacecraft into orbit, a task typically accomplished by relatively high thrust chemical rocket engines. Depending upon the requirements of the propulsion system, the thrusters must operate within a desired power regime and provide a specific impulse level (i.e., impulse or force per unit of propellant mass consumed during a given time interval), level of efficiency and thrust suitable for its application. In the past, in addition to bi-propellant liquid and solid chemical rockets, conventional spacecraft propulsion systems have used monopropellant thrusters. Electrostatic ion thrusters also have been proposed for these purposes; however, to date, this technology has not proven to be sufficiently mature and reliable for commercial and scientific spacecraft applications.
The next-generation communication satellites will require alternative thrust systems that are a small fraction of the satellite mass. These thrusters must also operate in a low power range (200-700W), but must provide a moderate specific impulse (1000-3000s) and offer a thrust in the range of tens of milli-Newtons (mN). However, known electrical augmented thruster designs, such as arc-jet and resisto-jet thrusters, do not operate well at power levels below 1 Kw. Pulsed magnetoplasmadynamic (MPD) thrusters using plastics or other solid propellants have low efficiencies, typically under 30%, making them incompatible with the goal of reducing the spacecraft overhead payload mass. Although some progress is being made in the development of electrostatic ion thrusters, particularly those having a planar design, there are concerns about their efficiency and, more importantly, the lifetimes of lower power units. A particular problem with such thrusters is the erosion of electrical grids during operation.
Conventional planar ion thrusters use magnetic fields to confine the electrons used for ionizing the neutral propellant atoms. Aside from the present ion jet concept, no other thruster concept known to date is spherical, nor does any other thruster use an electron guide grid to oscillate electrons for the purpose of ion generation. Previous patents of interest, but of remote relationship to the present concept, include John P. Brophy's 3-grid accelerator system for an ion propulsion engine (U.S. Pat. No. 5,369,953), J. R. Kaufman's original electron bombardment thruster concept (U.S. Pat. No. 3,156,090), and R. Boyer and J. P. Journoux's gas ionization chamber concept (U.S. Pat. No. 4,468,564).
Accordingly, it is an object of the present invention to provide a design for an ion thruster which will reduce grid erosion and significantly increase thruster lifetime.
It is another object of the present invention to provide a hot ionized or neutrally shaped gas source design which is compact, providing a greater weight reduction advantage.
Another object of the present invention is to reduce neutral propellant gas leakage, thereby saving propellant and further reducing mass.
In addition, it is an object of the present invention to provide a design for a source of hot ionized gas or neutrally charged gas for industrial applications where plasma spray, vapor deposition, or intense plasma heating is desired.